: Despite a substantial body of evidence suggesting a diet high in fat/meat and low in fruit/vegetables as an important determinant of colorectal cancer risk, little is known as to what specific aspects of the Western diet are responsible for the increased risk. In this prospective study, the applicants seek to determine whether increased body iron stores and depleted folate status enhance colorectal cancer risk, as it was proposed recently. Iron, which abounds in high fat/meat diet, catalyses oxidation reactions to produce oxygen radicals that may be carcinogenic by inducing damage to DNA. Iron is often prescribed for minor anemia, especially to women, and is contained in many popular over-the-counter multi-vitamin/mineral pills. Folate, which is plentiful in vegetable and fruits, is micronutrient deemed essential to preserving the normal control of proto-oncogene expression. The proposed study will be a spin off of the New York University Women's Health Study, an ongoing NCI-funded prospective study of hormonal and environmental factors and chronic diseases in women. The availability of this resource will allow the investigators to conduct the proposed study in a very timely fashion by accessing blood specimens and epidemiologic information that has been obtained in advance of cancer diagnosis. The main objectives of this proposal are to assess whether (1) increased serum levels of ferritin and transferrin saturation which are the best available indicators of increased body iron stores; and (2) decreased levels of serum folate and increased serum homocysteine levles are associated with increased colorectal cancer risk in women. The findings from this study could provide scientific evidence to be utilized in design of future dietary interventions for primary prevention of colorectal cancer. In addition, the availability of baseline dietary data for all cohort members will allow the investigators to assess the relationships of dietary intake of folate and iron to subsequent colorectal cancer risk after adjusting for other macro and micro nutrients.